A Briton is one of two anti-whaling protesters who have been ‘assaulted and tied up’ on a Japanese whaling ship, it’s been claimed.

The Sea Shepherd Conservation Society activists are being detained on the Yushin Maru No 2, one of the Japanese whaling fleet currently in Antarctic waters, after boarding the vessel from the society’s ship Steve Irwin.

Sea Shepherd claimed that Briton Giles Lane, 35, and Australian Benjamin Potts, 28, were being held hostage and had been assaulted and tied to the radar mast by the whalers.

The volunteer crew members went on board the whaling ship to inform the captain the fleet was in violation of international conservation law and an Australian court order by “illegally” killing whales, Sea Shepherd said.

But the Japanese Institute of Cetacean Research said the two activists illegally boarded the research vessel and were taken into custody.

The institute’s director-general, Minoru Morimoto, said the men had not been harmed.

“Any accusations that we have tied them up or assaulted them are completely untrue,” he said.

“It is illegal to board another country’s vessels on the high seas. As a result, at this stage, they are being held in custody while decisions are made on their future.”

The pair went on board the whaling ship with a letter warning against its “illegal activities” in the waters of the Australian Antarctic Economic Exclusion Zone.

According to the conservationists, the whalers are in violation of international conservation law by targeting endangered whales in a designated sanctuary in violation of a global moratorium on commercial whaling.

The letter also informed the Yushin Maru captain that Australia had passed a court ruling barring Japanese whalers from the Australian Antarctic Economic Exclusion Zone.

Sea Shepherd said the Steve Irwin’s captain, Paul Watson, had notified Australian federal police he wanted to see kidnapping charges brought against the whalers.

The Sea Shepherd vessel has been in pursuit of the whalers since last month.